1. Field of the Invention
The present invention generally relates to a downhole tool for use in a wellbore. More particularly, the invention relates to a downhole tool for isolating a wellbore. More particularly still, the invention relates to an expandable tubular having an expandable or swelling sealing element for isolating a wellbore.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling a predetermined depth, the drill string and bit are removed, and the wellbore is typically lined with a string of steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well to a designated depth. An annular area is thus defined between the outside of the casing and the earth formation. This annular area is filled with cement to permanently set the casing in the wellbore and to facilitate the isolation of production zones and fluids at different depths within the wellbore.
Generally, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. Typically, perforations are formed in the casing at the anticipated depth of hydrocarbons. The perforations are strategically formed adjacent the hydrocarbon zones to limit the production of water from water rich zones close to the hydrocarbon rich zones.
However, a problem arises when the cement does not adhere to the wellbore properly to provide an effective fluid seal. The ineffective seal allows water to travel along the cement and wellbore interface to the hydrocarbon rich zone. As a result, water may be produced along with the hydrocarbons.
One attempt to solve this problem is to employ a downhole packer to isolate specific portions of the wellbore. The downhole packer may be installed as an open-hole completion to isolate a portion of the wellbore and eliminate the need of cementing the annular area between the casing and the wellbore of the isolated portion. Typically, the downhole packer may be formed as an integral member of the existing casing and installed adjacent the desired production zone.
More recently, expandable tubular technology has been applied to downhole packers. Generally, expandable technology enables a smaller diameter tubular to pass through a larger diameter tubular, and thereafter expanded to a larger diameter. In this respect, expandable technology permits the formation of a tubular string having a substantially constant inner diameter. Accordingly, an expandable packer may be lowered into the wellbore and expanded into contact with the wellbore. By adopting the expandable technology, the expandable packer allows a larger diameter production tubing to be used because the conventional packer mandrel and valving system are no longer necessary.
However, one drawback of the downhole or expandable packers is their lack of gripping members on their outer surfaces. Consequently, the outer surfaces of these conventional packers may be unable to generate sufficient frictional contact to support their weight in the wellbore. Additionally, the expandable packer may not provide sufficient seal load to effectively seal the annular area between the expanded packer and the wellbore.
There is a need, therefore, for a packer having a sealing element that will effectively seal a portion of a tubular or a wellbore. There is a further need for a packer that will not reduce the diameter of the wellbore. Further still, there is a need for a sealing assembly that will effectively isolate a zone within a tubular or a wellbore.